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Flashcards in Implant Technology Unit 5 Deck (154):
1

when is joint replacement in the upper limb indicated

after other forms of conservative treatment have failed i.e. NSAIDs, injections

2

what is the primary and secondary aim of upper limb joint replacement

primary
- eliminate pain

secondary
- restore function to the particularly joint being replaced w/ a view of restoring overall functions of the hand

3

patients w/ RA often have several joints affected by the disease and require individual Tx plans - a problem w/ the spine or lower limb that require surgery is given priority over a problem in the upper limb, why?

- RA of the cervical spine causes instability and can be associated w/ significant or progressive neuro Sx.
- Needs to be addressed to prevent permanent damage

- successful replacement of hip and knee will lessen/eliminate need for upper limb to support BW during walking
- if these loads are not reduced/eliminated they could potentially compromise success of the surgery

4

if several upper limb joints are affected, and all joints are equally affected by pain, then as a general rule what order with joint replacements usually be performed

distally to proximally

i.e. fingers first, wrist, elbow and finally the shoulder

5

what is the reasoning for some surgeons working distal to proximal

- primary objective of upper limb joint replacement, after pain relief, is to allow restoration of hand function

- impairments in distal joints may compromise the critical, early physiotherapy necessary following the replacement of a more proximal joint

- arguable that more functional improvement is gained the more distal the joint

6

some surgery prefer to replace the shoulder however, before other distal joints, what are the reasons for this

- shoulder pain is more troublesome at night and may radiate to the elbows

- an immobile shoulder will cause abnormal loadings at the elbow which may lead to early failure of an elbow prosthesis

- rehab of the other upper limb joints can be simplified with a pain free or near pain free shoulder

7

what is the general criteria for upper limb joint replacements

- tolerate by human body w/ no short term and little long term risk

- relieve pain and achieve sufficient mobility for activities of daily living

- function w/out failure, ideally should last the expected life span of the individual patient

- insertion w/ predictable outcome guaranteed by competent surgeon

- cost effective

8

what is unexpected about the different between a total and hemi-arthroplasty in shoulder replacements

get better pain relief and ROM w/ total arthroplasty as opposed to hemi-arthroplasty

9

what is proving to be the superior joint replacements in the upper limb

shoulder joint replacements are proving to be more successful in survival terms

[followed by elbow, then wrist, then fingers]

10

what are 6 materials used in upper limb joint replacements

stainless steel
titanium
titanium alloys
cobalt chrome alloys
polyethylene (usually UHDP)
silicone elastomer

11

how often is shoulder replacements done

they are now the third most common arthroplastic procedure after hip and knee joint replacement

12

what is 1 way designs of shoulder prostheses are divided and what are these categories

divided according to the amount of movement constraint

1 - unconstrained e.g. Neer Prosthesis

2 - semiconstrained e.g. Gristina prosthesis

3 - constrained e.g. Michael Reese prosthesis

13

what is another way designs of shoulder prostheses are divided

may also be divided according to whether or not they conform to anatomy of the normal joint

1 - reversed or inverted anatomy design
- called as such as the humeral component is a socket instead of a ball
- e.g. Cavendish prothesis

14

what is the aim of most shoulder joint replacements

pain relief

improvements in ROM and function

most patients have RA or OA

15

what is the success rates of shoulder replacements

almost 90% have no or only slight pain after a total shoulder replacement

patients generally achieve around 90 to 135 abduction w/ unconstrained designs

16

what will the type of shoulder replacement design used depend on

quality of the soft tissue that surround the shoulder joint and provide joint stability

patients will undergo preoperative assessment of ROM, strength, stability and function to determine the exact nature of their problems

17

what shoulder replacement design will be used if the rotator cuff is intact and functioning

unconstrained prosthesis

18

what shoulder replacement design will be used if there is little or no stability provided by soft tissue

constrained design

19

what is the primary function of the shoulder

allow the hand to be positioned in space

20

what are the 3 synovial joints that make up the shoulder joint and 1 important articulation

3 joints
- glenohumeral, acromioclavicular and sternoclavicular

1 articulation
- scapulothoracic bone-on-muscle-on-bone articulation

21

what is the most important synovial joint in the shoulder which is the joint that is replaced in a total shoulder replacement

the glenohumeral joint
- as it has the largest ROM and most load bearing
- forces here can be as high as several times BW which a prosthetic must be able to withstand

22

what makes the shoulder joint very mobile but also very unstable

[what exists to make the shoulder more stable]

the shallow glenoid fossa

[the rotator cuff and other soft tissues]

23

what needs to be taken into consideration when the bone stock is removed during a TSR

that soft tissue attachments are preserved

[scapula is a thin bit of bone so there is only limited amount of bone stock to which a prosthetic can be attached]

24

what problems does the thin nature of the scapula cause

loosening of the glenoid component, especially w/ constrained design

25

what is the stability of an unconstrained shoulder prostheses, designed by Charles Neer, dependant on

intact, functioning rotator cuff mechanism

26

what are features of the design of the unconstrained shoulder prostheses

very nearly anatomical in shape and allows max potential function

achieves good pain relief

design requires only a min amount of bone to be removed [ensures soft tissue attachments are preserved]

27

what is the level of function in unconstrained shoulder prostheses dependant on

quality of the patients rotator cuff and deltoid muscle

28

the addition of a glenoid component w/ unconstrained shoulder prostheses has proved to be superior that those w/out it, w/ increased patient satisfaction, ROM and pain relief seen - but what is the disadv of this

risk of loosening of glenoid component

important factor in younger patients given the difficulty of revision operations

29

what is the stability of semiconstrained shoulder prostheses dependant on

rotator cuff mechanisms though some constrained is built into its design

30

in semiconstrained designs the glenoid component of constrained prosthesis is shaped so that it roofs over the superior aspect of the humeral component - what is this called and what does is resist

called Hooded Glenoids

resist upward shear force produced when the arm is elevated

thus prevents upward subluxation of the humerus that can occur when there is rotator cuff weakness or absence, and avoids tearing of the supraspinatus tendon

31

what is an example of a semiconstrained design

Gristina prosthesis

32

what is the disadv of semiconstrained designs

motion is limited compared to unconstrained

greater forces are transmitted to the glenoid component bone-cement junction resulting in more frequent loosening of the glenoid component

33

what are the biomechanical aspects of a semiconstrained shoulder replacement

- As the arm is elevated the muscle forces tend to pull the humerus upward, but this is prevented by the hood.

- ROM of the shoulder is restricted by the hood as during elevation the prosthesis or intact bone/soft-tissues will come into contact with hood.

- forces that act vertically on the hood produce moments about some point which must be counteracted by additional forces at the bone-cement junction.

- These forces tend to give rise to compressive stresses superiorly and tensile stresses inferiorly.

34

what movements are reduced in patients w/ semiconstrained shoulder replacements WITH a hooded glenoid component

reduction in external and internal rotation post-op

and achieve 15 degrees less flexion and abduction than patients w/ regular glenoid component

35

What material is used to construct the glenoid component of a Neer type shoulder prosthesis

Polyethylene

36

How could an unconstrained design be converted to a semi- constrained design

by using a hooded glenoid

37

disadv of a semiconstrained shoulder prosthesis compared to unconstrained one

restricted ROM

more freq glenoid component loosening

38

what are constrained total shoulder replacements mostly and what are the 3 current designs

ball in socket designs

[either normal anatomy or reversed anatomy [i.e. glenoid ball and humeral socket] ]

3 designs
- Stanmore, Michael Reese and Trispherical

39

what are features of the Stanmore design

metal on metal design

cup-shaped glenoid socket is fixed with three pegs and an abundant amount of bone cement

The humeral component is also cemented in place.

Once in position the two components are snapped together.

40

what are complications of the Stanmore constrained design

unsnapping of 2 components

instability

glenoid component loosening

41

what are features of Michael Reese constrained design

- cobalt-chromium humeral-head component and a polyethylene socket which fits within a metal glenoid cup.

- diameter of the lip is slightly smaller than that of the humeral head so that the ball is captive (i.e. it is a ball-in-socket design).

- designed to allow the humeral head to dislocate when a specified large moment (torque) is reached, so to prevent a # of the scapula occurring

42

what is disadv of Michael Reese constrained design

As with most constrained designs, impingement of the humeral component on the glenoid component occurs which restricts ROM

43

what is unusual about the Trispherical constrained design

made of 3 balls not 1

44

the trispherical design consist of a humeral and glenoid component both with a metal ball which are both then contained within a third larger polyethylene ball - what is this encapsulated within and what does this allow

encapsulated with a vitallium shell for extra strength


design allows for a greater ROM and avoids impingement of the prosthetic component

45

what is the ROM of a single ball-in-socket prosthesis related to

size of the head

the larger the head the greater the ROM

however, ROM is limited by the size of the joint space, by the need to ensure that the socket is of adequate thickness and by the requirement that the ball does not dislocate [Trispherical design partially overcomes these limitations]

46

in practice, what causes constraint in ROM

the surrounding soft tissue rather than the prosthesis itself

47

what is a reversed anatomy shoulder replacement joint and what are examples of it

socket on the humeral side and ball on the glenoid side of the joint

e.g. Kessel, Fenlin, Reeves

48

what is the rationale behind reverse anatomy joints

increasing the radius of the ball it would improve the ROM

theoretically, these designs have a better lever arm for the deltoid

49

what is the disadv of reverse anatomy shoulder replacement joints

more stress at the bone-cement junction

50

what causes difficulty in fixing the glenoid component in the shoulder joint

the small quantity of bone in the scapula

51

what are methods to securing the glenoid component to the scapula

All use large amounts of bone cement

- triangular shaped keel [Neer unconstrained]

- extended keel [trispherical design]

- pegs [Stanmore ball in socket]

- stem [Liverpool and Cavendish reversed ball in socket design]

- wedge [Fenlin reversed ball in socket design]

- large screw [Kessel reversed ball in socket design]

- flanges bolted to the base of the spine of the scapula [Kolbel reversed ball in socket]

52

the Neer design has an optional metal backed glenoid component, what is this thought to do

increase fixation and aid stress distribution

53

why do constrained designs tend to have more elaborate glenoid fixation

to secure the component against the larger loads present in this type

54

what is the Bickel designs method of securing the glenoid component

glenoid component is cemented entirely within the glenoid to maximise the contact area

55

what loosens more in a shoulder joint replacement - the humeral or the glenoid component

glenoid component
- 8 times more than humeral component

56

what design is predominantly used for constrained total shoulder replacements

A ball-in-socket design

57

what is the primary indication for elective replacement of the elbow joint

pain relief , with restoration of stability as the secondary indication

[rarely is restoration of motion primary indication]

58

what do most elective patients suffer from in elbow joint replacements

RA

[some OA and post-traumatic arthritis]

59

what are the primary functions of the elbow joint

the positioning of the hand in space

to allow the forearm to act as a lever

for some, acts as a weight bearing joint e.g. those who use a walking aid

60

what are the 3 articulations of the elbow joint

- the humeroulnar (trochleo-ulnar)

- the humeroradial (radiocapitellar),

- the proximal radioulnar

61

what forces does the elbow withstand

6 times body weight during dynamic activities e.g. throwing

3 times body weight during static loading

62

what are the functions of the 3 articulations in the elbow joint

the humeroulnar articulation carries the majority of the load

the humeroradial and proximal radioulnar provide additional stability

63

what position is the elbow in in anatomical position

full extension

64

when the elbow is at full extension what angulation is there

10 to 15 degrees valgus angulation (outward angulation) in relation to the upper arm

65

what happens to the angulation at the elbow as it flexes and what does this mean

it reduces to a few degrees of valgus or varus angulation at full flexion

thus, the coronal plane angle between the upper arm and forearm is not fixed but varies

66

why are uniaxial hinge prosthesis in elbow joint replacement unsuccessful

they maintain the same coronal plane angle between the upper arm and forearm giving rise to excessive shearing forces at the bone-cement interface and subsequent loosening

67

what is the ROM the elbow CAN achieve and what is needed for ADL

Can achieve;
F - 140 degrees
P - 70 degrees
S - 80 degrees

ADL:
F - 30 to 130 degrees
P - 50 degrees
S - 50 degrees

68

what provides the stability of the elbow joint

provided equally by congruity of the joint surface

and by soft tissues [anterior capsule, medial and lateral collateral ligaments, muscles]

69

what position is the elbow in during most ADL

flexed

70

when the elbow is flexed what is providing over 50% of joint stability

the medial collateral ligament

71

what happens if the radial head is removed in an elbow joint replacement

reduces the joint congruity so the Medial collateral ligament must resist all VALGUS loads entirely

thus, it is important to maintain as much of the surrounding soft tissue as possible during an elbow joint replacement to minimise stresses at the bone-cement interface

72

what is the loading at the elbow to some degree dependant on

the stiffness of the shoulder joint

if someone w/ total elbow replacement has a stiff shoulder joint and tries to internal or external rotate the arm, the stiffness at the shoulder will increase the rotational stresses at the bone cement interface

[one reason why replacement of the shoulder may be given priority]

73

what is the difference between first generation and second generation elbow joint replacements

first generation
- simple, uniaxial hinges

second generation
- unconstrained design

74

what is the other names of first generation elbow joint replacements and what was the first success one called

constrained or hinged designs

the Dee design was first successful total elbow prosthesis

75

what is the construction of the Dee design

- 3 cobalt chrome parts, the humeral component, the ulnar component and the axis pin

- axis of rotation was at right angles to the long axis of the humerus and ulnar; possible ROM 0 to 150 degrees flexion

- single axis meant carrying angle of the elbow was essentially lost

- stems of humeral and ulnar components were curved to fit the medullary cavities of the humerus and ulna

- both stems were convex anteriorly and in addition the ulnar stem was curved convex laterally [meant both left and right hand ulnar components were required]

- stems retained in place with PMMA bone cement

- additional keying point provided by means of metal buttons at base of humeral stem and undersurface of ulnar platform

76

the Dee design gives excellent pain relief and good motion, however it is unsuccessful, why?

long term deterioration due to loosening of the prostheses

due to restricted single axis motion forces upon the elbow by the prosthesis

unnatural motion gives rise to excessive shearing forces at the bone-cement interface

also high amount of metal wear debris from the metal on metal articulations also contributed to loosening

77

what was another complication with the Dee design apart from loosening

required removal of large amount of bone stock causing loss of attachments of stabilising soft tissue

caused additional stress to the bone cement interface

loss of bone stock also meant that when a prosthesis failed it was extremely difficult to salvage the joint

78

the Dee design has been abandoned and is rarely used now, when might it be used

occasionally for revisions and for patients w/out sufficient ligament or soft tissue competence

79

what are the 2 main types of second generation elbow prostheses [and a recent new variation]

1 - semiconstrained metal-to-polyethylene hinge types

2 - unconstrained metal-to-polyethylene resurface types

[designs that also resurface the radial head]

80

what do semiconstrained elbow designs usually consist of and what are examples of some

stemmed humeral and ulnar components with a hinged-like metal-to-polyethylene articulation

e.g. Pritchard-Walker, Coonrad and Tri-Axial prostheses

81

what do semiconstrained elbow joints allow

varying degrees of side-to-side laxity

some times referred to as "sloppy hinged" prostheses

82

what is the design of a tri-axial elbow prosthesis

semiconstrained design

loose fitting metal-to-polyethylene hinged articulation with long humeral and ulnar metal stems

hinged articulation has around 5 degrees varus laxity and 6 degrees valgus laxity

83

what load is needed to pull apart a Tri-Axial elbow prosthesis

50N
[unlikely to happen]

84

what does outcomes of the Tri-Axial elbow prosthesis dependant on

the patients condition

90-95% RA patients had complete pain relief
80% for OA and post traumatic arthritis patients

85

what is the general design of unconstrained elbow replacements and examples of the design

resurface the lower end of the humerus and olecranon

aim being to reproduce the anatomical structure and by doing so achieve normal elbow function and contribute to joint stability

examples
- Ewald (capitellocondylar), Kudo and the Souter- Strathclyde.

86

what does the Souter-Strathclyde prosthesis consist of

2 components :

- humeral component, which replaces the articulating surface of the humerus, made of Vitallium

- ulnar component, which replaces the articulating surface of the ulnar, made of high density polyethylene

87

what is the success rate of unconstrained designs in elbow joint replacements

90% of patients achieve good or excellent results

rates of dislocations 3-8% = slightly higher than semi constrained design

rates of aseptic loosening 1-3% = lower than semi constrained

88

what are elbow prostheses that resurface the radial head attempting to do and examples of this design

gain benefits of load transmission stability that are afforded by humeroradial articulation

e.g. Pritchard, Voltz and early modification of the Capitellocondylar

89

what are the 3 components of the Pritchard elbow replacement

1 - the metal humeral component which replaces the articulating surfaces of the trochlea and capitellum;

2 - the ulnar component, consisting of a metal stemmed base and polyethylene spacer, which replaces the articulating surface of the ulna;

3 - the radial component, consisting of a metal stemmed base and polyethylene spacer, which replaces the articulating surfaces of the radius.

90

what can be selected in the Pritchard elbow replacement for optimum stability

polyethylene spacers are supplied in various thickness so surgeons can select correct size for optimum joint stability

91

why have the results with designs that resurface the radial head in elbow joint replacements been variable

difficulties in balancing the 3 articulations at time of op

The Voltz and modified Capitellocondylar prostheses have unsatisfactory rates of loosening and dislocation and are no longer recommended for use

92

How do semiconstrained elbow prostheses differ from the first generation of hinged elbow prostheses

they have "sloppy" hinges with varying degrees of side-to-side laxity.

93

By what other name is the Ewald prosthesis also known

capitellocondylar prosthesis.

94

What benefit may be gained from resurfacing the radial head

additional load transmission stability

95

what are the 2 types of wrist joint prostheses

flexible hinge

total wrist

96

what is the main indication for wrist joint replacement

pain associated with RA and OA

[correction of deformity arising from these conditions is also important consideration]

97

when is arthrodesis in the wrist a preferred option

when only radiocarpal joint is affected

especially for younger patients and for those which exert large and regular loads on their wrists

98

what does the wrist joint include

extends from metaphyseal portion of the radius to the CMC joints and incorporates the 8 carpal bones

the carpal bones are interconnected by a complex network of extrinsic and intrinsic ligaments

the ligaments, particularly the extrinsic ones, are integrated into surrounding wrist capsule

99

how many tendons run across the wrist

24

[strong flexor tendons are positioned within the carpal tunnel formed by transverse arch arrangements of the carpals]

100

the distal radioulnar joint is usually considered separate from the wrist, what is its function and why is it considered in wrist joint replacements

forearm supination and pronation

most diseases that involve the wrist joint also involve this joint and must be taken into account in total wrist joint replacements

101

what is done if the distal radioulnar joint is diseased in a total wrist replacements

typically around 1cm of distal ulna is excised and the remaining distal ulna is carefully stabilised w/ soft tissues

102

where is the overall composite motion of the wrist centred

on a fixed point on the capitate through which the axes of rotation for both flexion-extension and abduction-adduction pass

essential that prostheses are precisely positioned so that the natural joint motion is reproduced, thereby assuring a better balance between the wrist extensors and flexors.

103

what is the ROM possible at the wrist

80-90 degrees flexion

70-80 degrees extension

35 degrees adduction

15-20 degrees abduction

104

what is ROM needed for ADL at the wrist

10 degrees flexion

35 degrees extension

105

what movement is essential at the wrist for ADL

extension

reason why wrist is set at around 20 to 30 degrees of extension during arthrodesis

106

what joint is an important contributor to the overall motion of the wrist and why

radiocarpal joint [a condyloid joint]

it has a greater radius of curvature for abduction-adduction than for F-E which provides more stability in the abduction-adduction plane

the smaller radius for F-E provides less stability but a greater arc of motion

107

what is the problem will ball and socket type wrist joint designs

they have a reduced radius of curvature for abduction-adduction which makes it difficult maintaining stability in the abduction-adduction plane

108

the complex relationship between carpal bones and overlying tendons is poorly understood - what is particularly important consideration

how the carpal tunnel maintains the strong flexor tendons close to the axis of rotation of the wrist joint, thereby decreasing their moment about the wrist joint

109

what was the flexible hinge joint prosthesis introduced for

for use in combo w/ resection arthroplasty

110

what is the design of the flexible hinge wrist joint prosthesis

has a proximal and distal stem with a barrel - shaped midsection

1 stem is inserted into the medullary canal of the distal radius and the other is inserted into the 3rd metacarpal through the partially resected capitate

111

what is the flexible hinge wrist joint prosthesis composed of

high performance silicone elastomer (rubber)

the implant may be used w/ or w/out titanium bone liners (grommets)

silicone rubber spacer that helps maintain an adequate joint space and overall wrist alignment

112

is the flexible hinge prosthesis a total prosthesis ?

no it is a resection arthroplasty with interposition of a silicone rubber spacer

113

what develops around the midsection in flexible hinge prosthesis after a period of time

a new capsulo-ligamentous system

114

what is the success rate of the flexible hinge prosthesis

60% of patients maintain good clinical results 5 years post op

post-op ROM is not improved but arc of motion is changed to a more functional range than that preop.

115

what % of flexible wrist prostheses have been found to tear on the sharp bony edges of medullary canals

20%

116

what are the 2 types of cemented wrist prostheses called and there design

Meuli - ball and socket type

Voltz - non-spherical "ball" and shallower socket

117

what is the composition of the Meuli prosthesis

- distal component with eccentric prongs that are inserted into 2nd and 3rd metacarpals

- twin pronged radial component

- polyethylene ball

- ball is fitted on to the radial component and articulated with the distal component

- ball is not constrained and so permits slight distraction of the prosthesis

118

what are the adv and disadv of the Meuli ball and socket design

disadv
- relies on adequate and proper soft tissue balance to prevent undesirable rotatory motion

adv
- avoids possibility of rotational failures of the prosthesis
- stresses on the anchorage of the distal and radial components are reduced because impingement can occur only at extremes of motion

119

what is the major modification that the meuli prosthesis underwent

replacement of a single stem for the radial component with 2 prongs

and the offsetting of the "prongs" or stems of the distal component

120

what does the Voltz prothesis consist of

3 parts

1 - metacarpal component with a single stem that is inserted into the 3rd metacarpal

2 - single stem radial component

3 - polyethylene cup

[cup is mounted on the radial component and articulated with the metacarpal component]

121

what is the shape of the polyethylene cup in the Voltz prothesis

cup is not a true sphere but rather a segment of a torus with a larger radius of curvature for abduction-adduction

122

what does the design of the shape of the polyethylene cup in the Voltz prothesis allow for

design mirrors the normal radiocarpal joint and restricts the max range of motion to 90 degrees F-E and 50 degrees Abd-Add

123

what modification did the Voltz prothesis design undergo

number of stems has been reduced

124

what did many patients develop because of the Voltz and Meuli wrist replacement

developed ulnar deviation deformities due to the increased moment arms of the ulnar wrist tendons

caused by the sitting of the prothetic centre of rotation radial to the normal wrist's centre of rotation

the modifications of both designs have attempted to shift the prosthetic centre of rotation so that it aligns more closely w/ normal wrist axis

125

what is the success rate for total wrist prostheses

similar to those for flexible prosthesis in terms of pain relief and maintenance of pre op ROM

126

what issues have been seen in the Meuli design and in the Voltz design

incidence of stem loosening and stress-shielding of the distal radius has found to be as high as 50% with the Meuli prosthesis

Loosening has been less frequent with the Voltz design, with incidence of around 25%, though bone resorption under the radial collar has been found in around 80%

127

How is wrist rotation prevented in the Meuli prosthesis?

Wrist rotation is prevented in the Meuli prosthesis by the correct and adequate balancing of the surrounding soft tissue

128

Which normal wrist articulation does the Voltz prosthesis resemble

radiocarpal joint

129

What are the two main problems associated with total wrist prostheses

loosening

stress-shielding of the distal radius

130

what is the most frequently indicated hand joint replacement

replacement of the metacarpophalangeal (MCP) joint

131

what are the 2 types of MCP joint replacement

flexible hinge

total MCP

132

what is the main indication of MCP joint replacement

pain and deformity associated w/ RA

some patients may have impaired hand function secondary to soft tissue imbalance [but w/ minimum discomfort]

133

what may be a preferred option for the MCP joint in younger patients requiring a strong pinch

arthrodesis of the index finger
- fused at around 40 degrees of flexion

134

what is the features of the MCP joint

condyloid joint formed by the ovoid head of the metacarpal and the elliptic cavity of the base of the proximal phalanx

joint is surrounded by joint capsule, collateral ligament, fibrocartilaginous palmar plate and muscle tendons [All of these contribute significantly to the stabilisation of the joint]

135

what is ROM of the MCP joint

3 planes of movement: F-E, Abd-Add and a small amount of Pro-Sup

major motion occurs in sagittal plane w/ around 0-90 degrees flexion

overall, the MCP contributes almost 80% of total finger flexion arc

[restricted MCP motion can therefore significantly impair hand function]

136

what was the flexible silicone elastomer hinge prosthesis for MCP joint replacement designed for

an adjunct to resection arthroplasty and relies on encapsulation to help maintain alignment

137

how is the flexible hinge MCP joint replacement inserted

inserted into the hollowed medullary canals of the metacarpal and proximal phalanx once adequate soft tissue and bone are resected to ensure that the implant functions freely

138

how does the flexible hinge MCP joint replacement move

stems are not fixed so the joint flexes and extends they glide within the medullary canals

piston-like motion thought to be beneficial in terms of more even force transmission and increased ROM

139

what may or may not be added to flexible hinge MCP protheses and why were they introduced

titanium bone liners (grommets)

introduced to shield the implant from sharp bone edges after high tear rates has been recorded

press-fitted (interference fitted) into position

140

what is the success rate for flexible hinge MCP prostheses

70-80% patient satisfaction

141

what happens if a fracture occurs with flexible hinge MCP prostheses

the prosthesis need not always be replaced as the joint often continues to have pain-free motion and remain stable

142

what are examples of a total MCP joint replacements and how are they designed

Steffee, Schultz, Strickland

all of these incorporate a metallic component that articulates with a polyethylene component

both components are cemented in to the medullary canals

143

what are the problem associated with MCP total joint replacements

implant fracture
migration
loosening

144

total MCP joint replacements do not yet provide consistent results compared to the flexible hinge replacements - however, when is a total MCP joint replacement preferred

younger patients who would wish to perform manual tasks that place higher demands on the MCP joints

145

what is the main indication for interphalangeal (IP) joint replacement

pain and deformity associated with RA, degenerative arthritis and post-traumatic arthritis

[Implant arthroplasty of the distal interphalangeal joint is rarely indicated, since this joint contributes far less to the overall finger motion]

146

what is preferred procedure for DIP joints

arthrodesis as more reliable procedure and results in only min functional deficit

147

what are the 2 types of IP joint replacement

flexible hinge

total interphalangeal

[actual protheses are same as those used for MCP joints but have smaller dimensions]

148

what problems does replacement IP joints face

same problems as MCP joint replacements

[implant fracture, migration and loosening]

149

what is the features of the proximal and distal IP joints

bicondyloid joints

formed by the 2 condyles of the more proximal phalanx and the corresponding cavities of the more distal phalanx

joints are stabilised by bony articulation itself and surrounding soft tissues (joint capsule, collateral ligaments, the fibrocartilaginous palmar plate and muscle tendons)

150

ROM for PIP and DIP

major plane of motion is sagittal plane for flexion-extension

PIP
- 0-110 degrees flexion

DIP
- 0-90 degrees flexion

PIP contributes 85% of interphalangeal motion
DIP 15%

[therefore, preservation of PIP joint motion is far more critical than that of DIP joint]

151

what is the success rate for flexible hinge prostheses in PIP joints

PIP joints have satisfactory pain relief in 98% of cases

40-60 degrees ROM expected

0.5% infection rate [rare]
5% fracture rate

152

what is the name of the highly successful finger joint replacement

Swanson flexible hinge prosthesis

153

what is the preferred shoulder joint replacement method

unconstrained prostheses, provided good condition of surrounding soft tissues, particularly the rotator cuff

154

why is wrist joint replacements the least established of larger upper limb joint replacements

the high rate of loosening